Surface Floating 2D Bands in Layered Nonsymmorphic Semimetals: ZrSiS and Related Compounds

Abstract

In this work, we present a model of the surface states of nonsymmorphic semimetals. These are derived from surface mass terms that lift the high degeneracy imposed on the band structure by the nonsymmorphic bulk symmetries. Reflecting the reduced symmetry at the surface, the bulk bands are strongly modified. This leads to the creation of two-dimensional floating or unpinned bands, which are distinct from Shockley states, quantum well states, or topologically protected surface states. We focus on the layered semimetal ZrSiS to clarify the origin of its surface states. We demonstrate an excellent agreement between density functional theory calculations and angle-resolved photoemission spectroscopy measurements and present an effective four-band model in which similar surface bands appear. Finally, we emphasize the role of the surface chemical potential by comparing the surface density of states in samples with and without potassium coating. Our findings can be extended to related compounds and generalized to other crystals with nonsymmorphic symmetries.

Electron-phonon coupling and Kohn anomaly due to floating two-dimensional electronic bands on the surface of ZrSiS

“…Two kinds of nonsymmorphic symmetry can be recognized: a glide mirror in the plane formed by the square nets of the Si atoms and two screw axes C 2x (C 2y ) along the a(b) directions in the Si layer. The nonsymmorphic symmetry with glide mirror is crucial for the formation of the robust Dirac cone below E F 47 as well as the surface floating 2D bands 43 . The weak bonding energy between the two adjacent Zr − S layers 65 allows easy cleavage along the ab planes to obtain the (001) surface.…”

“…1(e), the calculated Fermi surface on the SBZ illustrates the surface floating 2D bands. Such surface states show as ellipses aroundX at the Fermi energy and shrink nearly linearly to a vertex at around 350 meV below the Fermi level43,45,48 , as demonstrated inFig. 1(f).…”

“…However, despite the topological nature in its bulk band, it turns out the surface states of ZrSiS are not derived from the bulk topology. Instead, they are highly 2D, floating on top of the bulk, merely due to a reduced symmetry at the surface 43 . Consequently, it is natural to expect the unique surface states would also interact with phonons and show anomalies in surface phonon dispersions.…”

Surface termination dependent quasiparticle scattering interference and magneto-transport study on ZrSiS

“…This is mainly because the disorder from the large amount of impurities on the Si-surface suppresses the QPI. In addition, the surface band near X has significant S-p orbital contribution and the dispersion towards G and M is linked to a change in its Zr-d orbitals [31], which reduces the spectral weight on the surface bands and in term, weakens the QPI near X on the Si-surface. To quantify the QPI data, we then extract q 1 and q 2 from the dI/dV(q, E) maps taken on both surfaces (see figures 4(b) and (c)), in which both q-vectors exhibit the identical energy dispersion on both surfaces within the overlapped energy range and agree well with our calculated band structure.…”

Electron-phonon interaction and zero-field charge carrier transport in the nodal-line semimetal ZrSiS

“…This makes this material an excellent candidate for studying Dirac fermions. ZrSiS has been extensively studied experimentally, demonstrating exotic physics and rich spectrum of remarkable properties [12][13][14][15][16][17][18][19][20][21][22][23][24]. Among them are strongly nested Fermi surface [12,13], strong Zeeman splitting [22], topologically * a.rudenko@science.ru.nl † s.yuan@whu.edu.cn nontrivial states [14][15][16], high carrier mobility [17,18], frequency-independent optical conductivity [23], and unconventional mass enhancement of quasiparticles near the nodal line, as indicated by quantum oscillations measured in high magnetic fields [24].…”